Richard S. Cowan

Prediction of Failure Transitions in Sliding Contacts by a Thermomechanical Wear Model

A wear equation in general form is offered by which the transition between mild wear and severe wear is identified. This wear criteria equation is governed by three nondimensional parameters: Fo, C T , and G t , which are measures of time, material property dependence on temperature, and thermal stress intensity, respectively. From this equation, wear maps are constructed. Along with results from Hertzian contact theory, the wear criteria equation and wear map can be used for design guidance. As an example, AISI 52100 steel is examined by comparing calculated data, based on a thermomechanical wear model, with experimental results of sliding contacts. The critical temperatures at which thermomechanical wear can occur are also calculated

Surface engineering... an enigma of choices

In order to generate the optimum surface, without negatively influencing the desired properties of the subsurface material, a myriad of surface selection techniques are available to choose from. This paper provides an overview of these methods, by broadly classifying the surface and overlay coating treatments currently used, according to the fabrication styles of atomic deposition, bulk deposition and direct surface modification. Insight into the research, development and utilization of these concepts, so as to address the needs of surface engineers today and in the future, is offered.

Application of the Thermomechanical Wear Transition Model to Layered Media

Sliding surfaces in contact produce a stress field and frictional heat source which may induce severe wear from material yielding. The initiation of such thermomechanical wear will be influenced by a surface film, possessing different thermal and mechanical properties than those of the substrate. Conditions for layered systems that can be treated as monolithic, and therefore amenable to the application of the current thermomechanical wear transition model, are discussed considering thermal and isothermal effects. A range of layer thickness and material combinations are presented, such that when coupled with the conditions of operation can be used for design guidance. As an example, steel coated with titanium nitride is examined by comparing calculated data, based on the thermomechanical wear model, with experimental results.

High velocity wear: Experiments and modeling

Mechanical wear at high sliding speeds is an important consideration in designing more efficient and effective electromagnetic launcher components. Understanding the influence of sliding velocity, contact pressure, and material properties on wear rates is important in developing predictive models for design. A novel inertia loaded wedge experiment is employed at Georgia Tech to study wear at sliding speeds and contact pressures in excess of 1,000 m/s and 100 MPa for a 6061-T6 aluminum slider on a C110-H2 copper guider. Test results showed a transition from mild to severe wear took place at approximately 30.5 cm or 1,000 m/s, which corresponds to a mechanical heating rate of 100 × 109 N/m·s. Aluminum deposition on the guiders was quantified using a white light interferometer and plotted as a function of position and velocity. A normalized wear rate model in the severe wear region was developed.

Machinery Diagnostics: Fundamentals and Tribosystem Applications

Machinery Diagnostics deals with the “health” of machines – characterized by “structural integrity” and “functional performance” – and the examination of faults and failures by nondestructive evaluation. The aim of this chapter of the Tribologie-Handbuchis to present the fundamentals of machinery diagnostics and to apply them to tribosystems, which are technical entities containing interacting components in relative motion, subject to friction and wear. The presentation of failure prevention strategies includes root-cause analysis, statistical control, reliability engineering, and asset maintenance. Condition monitoring deals with vibration monitoring, oil monitoring, corrosion monitoring, thermal monitoring, and electrical signature analysis. The application of machinery diagnostics to tribosystems is exemplified with bearings, gears, seals, lubricants and hydraulic systems.

Finite Element Analysis of Contact and Structural Phenomena of a Lab-Scale Electromagnetic Accelerator

This work presents a finite element analysis (FEA) of the initial armature-to-rail contact of a lab-scale electromagnetic accelerator (12.5 mm rail height) and a modal analysis of the armature. Structural results of the von Mises stress, the contact pressure, and the contact area are presented with the vibrational characteristics (frequencies and mode shapes) of the un-stressed and the pre-stressed armature.© 2007 ASME

Condition Monitoring Tools for Tribologists

This paper addresses technologies for minimizing the impact and occurrence of critical failures in mechanical systems. Attention is focused on tools of use to a tribologist in detecting and identifying incipient material failures, predicting the occurrence of such failures, and monitoring the condition of a triboelement in real-time.